1. Field of the Invention
The present application relates to a multi-layered film, a method of forming the same, a backsheet for a photovoltaic cell and a photovoltaic module.
2. Discussion of Related Art
Recently, there are growing concerns on renewable and clean energy because of global environment problems and exhaustion of fossil fuels, and among these, solar energy has attracted attention as a representative pollution-free energy source which can resolve problems of environmental pollution and exhaustion of the fossil fuels.
A photovoltaic cell to which a principle of generating solar power is applied is a device for converting solar light into electric energy. Since the photovoltaic cell is necessarily exposed to an external environment for a long time to facilitate absorption of the solar light, the photovoltaic cell is formed in a unit type by performing various packaging processes to protect the cell. The unit is referred to as a photovoltaic module.
The photovoltaic module should use a backsheet having excellent weather resistance and durability to stably protect the photovoltaic cell when exposed to an external environment for a long time. The backsheet for a photovoltaic cell is in contact with ethylene vinyl acetate (EVA) used as a photovoltaic encapsulant so as to physically protect the photovoltaic cell, prevent moisture penetration into the cell and be maintained to be electrically insulated. Thereby, the photovoltaic module may be operated for 25 years or more without degradation of output characteristics. Accordingly, the backsheet for a photovoltaic cell should have excellent UV resistance and weather resistance, and excellent long-term reliability including less degradation of mechanical characteristics, moisture preventability and electric insulating properties during use.
To satisfy the above-described characteristics, currently, a product manufactured in a triple-layered structure in which a polyvinyl fluoride (PVF) film is stacked on both surfaces of a polyethylene terephthalate (PET) film is being widely used. However, the conventional art has a complicated manufacturing method and a problem of hydrolyzing an adhesive layer with moisture to adhere the PET film to the PVF film, and therefore it is difficult to maintain an interface adhesive strength with the long-term reliability.
In addition, recently, backsheets for a photovoltaic cell manufactured by processing another fluoropolymer such as polyvinylidene fluoride (PVDF), chlorotrifluoroethylene (CTFE) or ethylene chlorotrifluoroethylene (ECTFE) in the form of a film instead of the PVF film have been increasingly used, but the fluoropolymer still has a problem of a low adhesive strength.
For these reasons, there are ongoing demands for a backsheet for a photovoltaic cell which can have excellent durability and weather resistance while maintaining an adhesive strength for a long time, reduce a production cost due to a simple manufacturing method, and enhance productivity and quality of a photovoltaic module.